Language in C 面接の質問と回答

Question: How do I write a function that takes variable number of arguments?

Answer: The following program demonstrates this.

#include <stdio.h>
#include <stdarg.h>

void main( )
{
int i = 10 ;
float f = 2.5 ;
char *str = "Hello!" ;
vfpf ( "%d %f %sn", i, f, str ) ;
vfpf ( "%s %s", str, "Hi!" ) ;
}

void vfpf ( char *fmt, ... )
{
va_list argptr ;
va_start ( argptr, fmt ) ;
vfprintf ( stdout, fmt, argptr ) ;
va_end ( argptr ) ;
}

Here, the function vfpf( ) has called vfprintf( ) that take variable argument lists. va_list is an array that holds information required for the macros va_start and va_end. The macros va_start and va_end provide a portable way to access the variable argument lists. va_start would set up a pointer argptr to point to the first of the variable arguments being passed to the function. The macro va_end helps the called function to perform a normal return.